Now that we're getting into the second half of August, it's the the time of year when we really start to monitor the far eastern Atlantic for budding tropical waves that could potentially develop into tropical storms or hurricanes.

Now that we're getting into the second half of August, it's the the time of year when we really start to monitor the far eastern Atlantic for budding tropical waves that could potentially develop into tropical storms or hurricanes.

(CNN) -- British Prime Minister David Cameron described the airstrike that may have killed "Jihadi John" in Syria as an act of self-defense as he awaited confirmation that the jeering, sadistic ISIS mouthpiece is dead.

If the raid killed the man seen in numerous ISIS beheading videos, "it will be a strike at the heart" of ISIS, Cameron said.

"We always said we will do whatever is necessary to track down (Mohammed) Emwazi and stop him taking the lives of others," he said.

U.S. officials said "Jihadi John" may have been killed in a coalition airstrike in Raqqa, Syria. While the Pentagon, in announcing the strike Thursday night, wouldn't definitely say he was dead, U.S. officials said authorities are confident he was.

This was a mission of "persistent surveillance," a senior U.S. official said, adding that authorities knew it was Emwazi when they took the shot.

Emwazi was in a vehicle at the time of the strike, which was launched from a drone, another U.S. official said.

Cameron said the airstrike was the result of the UK working with the United States.

A top priority

Emwazi, a British citizen, was a most wanted man.

As the masked face of ISIS, he appeared in a series of brutal videos, dressed head-to-toe in black and holding a knife.

He took part in the murders of U.S. journalists Steven Sotloff and James Foley, U.S. aid worker Abdul-Rahman Kassig, British aid workers David Haines and Alan Henning, Japanese journalist Kenji Goto, and a number of other hostages, the Pentagon said.

The Ramadhan Foundation, a Muslim organization in the UK, said Emwazi was the manifestation of evil.

"The killing of Mohammed Emwazi in Syria is a significant moment in the fight to get justice for David Haines, Alan Henning and all the victims of this evil man," said Mohammed Shafiq, the group's executive director.

The strike

The strike appeared to have taken place Friday in Syria (Thursday night in the U.S.).

Syrian activists in Raqqa reported that four ISIS foreign fighters, including a leader with British nationality, were killed by coalition airstrike, the Syrian Observatory for Human Rights said.

Cameron was aware of the airstrike and notified families whose relatives were murdered by Emwazi.

"Britain has been working hand in glove with America over the 'Jihadi John' drone strike, to defeat (ISIS), and to hunt down those murdering hostages," Cameron's office said. "The Prime Minister has said before that tracking down these brutal murderers was a top priority."

A frequent video presence

Emwazi, who speaks English and is believed to have been born in Kuwait, was frequently seen in hooded hostage videos carrying out violent beheadings.

For periods at a time this year, Emwazi was not seen in hostage videos, though U.S. officials told CNN in July that they had learned that he was alive and hiding near Raqqa.

Analysts describe him as grotesque and fond of sadistic torture techniques, with one former hostage recounting last month how his captor made him dance the tango with him.

Friends of Emwazi said they believed he started down the road to radicalization when he traveled to the East African nation of Tanzania in 2009, The Washington Post reported this year.

He was supposed to be going on safari, but he was reportedly detained on arrival, held overnight and then deported. He was also detained by counterterrorism officials in Britain in 2010, The Post said.

Authorities have not disclosed the reasons for those reported detentions.

The Post's report includes emails Emwazi purportedly wrote after British counterterrorism officials detained him and stopped him from flying to Kuwait.

"I had a job waiting for me and marriage to get started," he wrote in a June 2010 email to Asim Qureshi, a member of the CAGE civil rights group, The Post reported.

But now "I feel like a prisoner, only not in a cage, in London. A person imprisoned & controlled by security service men, stopping me from living my new life in my birthplace & country, Kuwait," the email said.

Some terrorism experts said he was on a path toward extremism years before that incident.